1. Field of the Invention
This invention relates generally to electromagnetic induction suspension, propulsion, and stabilization systems for ground vehicles, and more particularly concerns an electromagnetic induction suspension and propulsion system for a vehicle utilizing superconducting magnets for electromagnetic levitation of the vehicle over a substantially planar guideway. Electromagnetic levitation involving induction by magnets on a moving vehicle interacting with passive conducting guideway elements is also referred to herein as electrodynamic levitation.
2. Description of Related Art
With an increasing need for transportation systems that can minimize environmental and noise pollution, that are more energy efficient, and that can reduce traffic congestion and improve travel safety, and with new advances in materials and technology, interest in passenger and freight vehicles suspended by magnetic levitation has also grown. Such systems have been proven in pilot projects to be able to achieve speeds of over 300 miles per hour.
Conventional wheeled systems have the disadvantage that vehicle speed is limited owing to the frictional interplay and mechanical stresses between the vehicle and the track system and within the wheel assemblies of the vehicle. Transfer of power from the track to the vehicle also becomes a limitation, and at high speeds, conventional wheeled ground vehicles become highly inefficient and subject to excessive dynamic mechanical stresses.
Vehicles suspended through magnetic levitation can have much reduced friction losses and mechanical vibration problems due to guideway irregularities because they do not contact the guideway.
Passenger transport systems based upon electromagnets have utilized magnetic attraction forces to suspend moving vehicles. However, magnetic attractive forces inherently result in a very unstable levitation of the vehicle above the guideway. To prevent crashes, it is necessary with such systems to maintain the distance between the vehicle and the guideway through feedback from a gap sensor. This sensor then controls electronic power supplied to rapidly adjust magnet current to constantly maintain the gap. Typical electromagnetic attractive systems commonly produce heavy vehicles with small clearances between the vehicle and the guideway. Such systems are known to rely on vehicle/guideway interfaces in which the vehicle mechanically captures the guideway. In fact, these magnetic levitation system designs require that the vehicle capture the guideway in order to develop vehicle lift upwards toward a ferromagnetic rail. Vertical stability and lateral stability require control currents for both vertical and horizontal directions. The need to capture the guideway has been assumed to be an acceptable safety measure to ensure that a high speed vehicle will remain safely on the guideway in the event of a malfunction resulting in a loss of levitation or control.
The opportunity to switch a vehicle between guideways in these systems, in order to change guideways or to move off-line to a passenger or light freight transfer platform, has been limited because the complex vehicle/guideway magnet interface served to mechanically capture the vehicle magnets. As a result, switching the path of a vehicle from one guideway to another required mechanically switching long sections of the guideway over a period of many seconds. Safety and secondary suspension systems have also served to prevent rapid switching of a vehicle from one guideway to another. In addition, mechanical guideway switching has required the vehicle to slow down far below its normal speed of 300 m.p.h., as well as elaborate and complex interlocks to ensure that the proper mechanical interfaces had been satisfied for safe switching.
Designs in which the guideway captures the vehicle between vertical walls limit the methods whereby the vehicle may be switched from a primary guideway onto a secondary guideway. One such system employs electrodynamic repulsive force when switching from a primary guideway to a secondary guideway at guideway-branch locations. This guideway system mechanically raises and lowers a guideway element to develop the repulsive force necessary to assist in switching between guideways. This is analogous to conventional rail cars relying on mechanically changing tracks to redirect the rail car onto a new track, however, in the vertical plane.
Another approach to switching has been proposed for switching a small-capacity magnetic levitation system which also employs electrodynamic force. In this system the weight of the vehicle is supported by the interaction between pairs of outrigger paddles extending horizontally from each side of the vehicle and wall-mounted rails. The design of the vehicle/guideway interface necessitates that the vehicle change its course by selecting a rail of a different vertical height along the wall at a switching junction. The vehicle then rises or falls vertically on the selected rail until clear of the switching junction and the non-selected rail.
It would be desirable to provide for an electromagnetic induction suspension and stabilization system which takes advantage of the electrodynamical forces between vehicle magnets and guideway to operate on a substantially planar guideway. It would also be desirable to provide a system which allowed electronic horizontal switching between guideways at high speed. A vehicle operating on a substantially planar guideway may therefore be horizontally switched from one guideway to another at high speed. In addition, switching between substantially planar guideways allows horizontal switching without cumbersome, and potentially hazardous, mechanical switching of guideway elements or vertical displacement of the vehicle. The present invention meets these needs.